This invention relates to brazing. More particular it relates to precious metal brazing compositions.
In brazing operations using precious metal brazing alloys the use of other materials in conjunction therewith to provide a desired joint thickness is disclosed in U.S. Pat. No. 2,606,362. In U.S. Pat. No. 2,606,362 tungsten particles having a diameter and thickness approaching that of the composite foil are disclosed. By use of these particles the proper spacing between the parts to be joined is maintained and the desired joint thickness is obtained.
Molybdenum has also been used as a constituent in silver-copper brazing alloys for joining tungsten parts. In Modern Metal Joining Techniques, Swartz, Wiley-Interscience, a division of John Wiley and Sons, New York, 1969, page 337, a number of brazes having liquidus temperatures of from 1200.degree. F. to 5500.degree. F. are disclosed. Three Ag-Cu alloys are disclosed which contain molybdenum. No percentages of constituents are given. Silver and copper do not alloy with tungsten. If the braze metal does not alloy with the parent metal being brazed, the joint will be strong at low temperatures but weak at high tempertures. Articles made from tungsten are normally used at high temperature application, therefore, it is believed that the molybdenum portion of the Ag-Cu-Mo alloys reported in Modern Metal Joining Techniques, supra, is present as an alloying ingredient to alloy with the tungsten that is being brazed.
Certain silver-copper brazing alloys are well known. In general such brazing alloys contain from about 40 to about 72% silver, from about 25% to about 40% of copper and may contain from about 5 to about 40% of metals selected from tin, cadmium, zinc and indium. Such alloys have liquidus temperatures in the range of from about 700.degree. C. to about 780.degree. C. As can be appreciated the costs of such alloys has risen dramatically during the past few years due to the cost of silver.
It is believed therefore that a brazing composition having essentially the same properties as the prior silver-copper brazing alloys but at an appreciably lower price would be an advancement in the art.